The DE-OS No. 2 755 575 relates to a laser operated character generator in which the laser beams that write the characters are generated in a single acousto-optical modulator, and the angles of diffraction of the beams are constant in time. In the acousto-optical modulator described in this publication, VHF oscillators are used and each oscillator is coupled through a respective control stage associated therewith to a respective ultrasonic transducer of the acousto-optical cell. The frequency of each oscillator determines the direction of the corresponding outgoing laser beam and its amplitude defines the intensity of this beam. The control signals applied to the control inputs of the control stages enable or inhibit the passage of the output voltages of the associated oscillators towards the corresponding ultrasonic transducers.
In equipment using acousto-optical modulators (e.g. in laser-operated character generators) outgoing laser beams with constant diffraction angles are generated, and these beams are deflected in a direction normal to the common plane of their generation by means of a separate deflecting means (e.g. by a swinging mirror or by an additional acousto-optical modulator). The position adjustment of the laser beams in their common plane of generation is carried out generally by means of an additional swinging mirror. Such a position adjustment can be used for compensating the effect of the fluctuation of the rotational speed of the recording cylinder.
It has been discovered that the field of application of acousto-optical modulators can be widened, if in addition to the laser beams leaving the acousto-optical cell with a constant diffraction angle, the generation of additional outgoing laser beams could be effected for which the diffraction angle of the additional laser beams could be changed according to a predetermined controlling program either with high or low rates without the need of using any additional active optical device.
It has been discovered furthermore, that it would be preferable if the common position adjustment of the outgoing laser beams within their common plane of propagation could be effected electronically in the same acousto-optical modulator rendering the conventionally used swinging positioning mirror to be unnecessary.
These advantages cannot be achieved with conventional acousto-optical equipment.
The object of the present invention is to provide a circuit arrangement for controlling an acousto-optical cell that on the basis of the acousto-optical modulator used in the DE-OS No. 2 755 575 can provide for the accomplishment of the above sketched requirements without the need of using additional active optical devices.